Gun sight



Oh? 290719066 5R Feb. 16, 1937. u. P. GATY GUN S IGHT Filed March 27, 1936 ATTORNEYS 33. GLUMUHHJL lllbl l'iulvlnu lo.

Patented Feb. 16, 1937 UNITED STATES PATENT OFFICE GUN SIGHT Application March 27, 1936, Serial No. 71,129

6 Claims.

This invention relates in general to gun sights and more particularly to front sights for ilexible machine guns.

In accurately aiming and firing a flexible machine gun at a moving or stationary target from a rapidly moving base, such as an airplane, allowance must be made for bullet drift due to the movement of the base except when the latter is moving in a direct line toward or away from the target. Bullet drift takes place along a line parallel to the direction of motion of the firing base, and for firing at targets at right angles to the direction of motion of the firing base the gun barrel must be moved through an arc toward the stern of the moving base a predetermined amount. The angle between the direct line of sight to the target and the axis of the gun barrel after such movement is known as the angle of deflection and is dependent upon the speed of the moving base and the position of the target relative thereto. Should the target be in a position other than at right angles to the direction of motion of the moving base, the gun barrel accordingly should be pointed so as to provide a smaller angle of deflection, depending upon the angular disposition of the gun, relative to the direction of motion of the moving base, when trained upon the target. Although the bullet drift is parallel to the direction of motion of the moving base, the direction of the eiective component of drift is at right angles to the axis of the gun barrel and it is in this direction that the correction for bullet drift must be made.

Compensation for bullet drift in ring a gun from a moving base requires the use of a sighting means that will provide the gunner with means for determining the magnitude of the correction to be made. The amount of the correction depends upon the speed of the base and the angular disposition of the gun relative to the direction of motion. These compensations are essential in order that the gun may be properly aimed to obtain a hit. It is also essential that the sighting means be capable of corrections over a wide range as the speed of the moving base is continually increasing or decreasing and as the position of the target continually changes with respect to the firing base it follows that the angular disposition oi the gun relative to the direction of motion of the ring base is continually being changed.

Because of these changes in speed of the firing base as well as the angular disposition of the gun relative to the direction of motion of its base, the provision of a satisfactory sighting means has oiered a very complex problem, heretofore not satisfactorily solved. Various sighting devices have been used in an eifort to provide the proper reference points but none of these devices have proven satisfactory. The sight most commonly used is the well known conventional wind vane sight, used during the World War period. This sight was designed to make automatic correction to the position of the front sight bead for various angles of fire from the moving platform. In other words, it attempted to give both the direction and the magnitude of the correction for the various angles but could only do so for a predeterminedly adjusted speed of the moving base. It is universally mounted, having a vertical axis of rotation and a horizontal axis of movement. A wind vane is actuated by the air passing the moving base to operate the correction means to keep it always parallel to the direction of motion of the iiring base. In order for this type of sight to operate correctly it must be manually adjusted to the speed of the moving base. It can readily be seen that such manual adjustment of the sight for every change in speed of the aircraft while in actual use on such a moving base is a physical impossibility. Therefore, the bead only indicates to the gunner the direction in which the sights should not be aligned, for any speed other than that for which the Wind vane sight has been adjusted. This type of sight is of further disadvantage in that the entire pantographic linkage mechanism and vane assembly is subject to rapid oscillation about the horizontal axis, due to slipstream turbulence. 'I'his produces a disconcerting vertical vibratory motion of the front sight bead and bead post. This vibration further interferes with the use of any reference point for aiming no deflection shots such as those directly ahead or directly astern. Other sights have been devised, all of which have one or both of the above-mentioned disadvantages. Other sights have not only included these disadvantages but have proved too complex and bulky for practical use.

It is, therefore, an object of this invention to provide a simple. light and efficient drift compensating front gun sight.

Another object is to provide an improved drift compensating front gun sight that requires no manual adjustment for changes in speed of the moving base supporting the gun.

Another object is to provide an improved drift compensating front gun sight that is free from vibration due to airstream turbulence caused by the movement of the gun base.

With the foregoing and other objects in view, the invention comprises the combination of parts and the details of construction hereinafter set forth in the following specification and appended claims, certain embodiments thereof being illustrated in the accompanying drawing, in which:

Figure 1 is a view in perspective of a machine gun with a rear ring sight and a front drift compensating gun sight.

Figure 2 is a view in rear elevation of the drift compensating front gun sight.

Figure 3 is a view in side elevation of the same.

Figure 4 is a diagrammatical illustration in plan of a moving firing airplane and a moving target airplane; illustrating the actual and apparent bullet travel and the bullet drift component.

Figure 5 is a diagrammatical illustration of the relative disposition of the sights for the problem represented in Figure 4, for one speed of the firing airplane.

Figure 6 is similar to Figure 5, for another speed of the firing airplane.

Figure '7 is a view similar to Figure 4 showing the moving firing and target airplanes flying in different directions and the gun being red at a high angle abaft the beam.

Figure 8 is a View similar to Figure 5 for the problem of Figure 7, at one speed of travel of the firing airplane.

Figure 9 is a view similar to Figure 8, for another speed of travel of the firing airplane.

Referring more particularly to the drawing, the improved drift compensating front sight comprises a post I, which is removably secured to the gun barrel 2. The post carries a pin 3 about which the sleeve 4 of the compensating sight assembly is rotatably mounted. This sight comprises a wind vane 5 and an arrow 6. For purposes of gradation the point of the arrow is indicated at I and the barb at 8. The arrow may be further graduated by markings or by pins such as 9. The sight is mounted near the outer end of the gun barrel so that the end 3 of the pin 3 faces the gunner in accurate alignment with the barrel. The sight is therefore capable of pivotal movement about only one axis, namely the pin 3, which is parallel to the axis of the gun barrel. The compensating sight is shown as being used in conjunction with a rear ring sight of the type shown in my application Serial No. 15,563, for Ring sight, filed April 10, 1935, and comprises an outer ring I0, and intermediate ring II and an inner, or peep sight, ring I2.

'I'he compensating sight provides the gunner with a line of reference along which the correction for bullet drift must be made. The magnitude of each such correction depends upon the speed of travel of the firing airplane and the angle at which the gun is pointed relative to the longitudinal axis thereof. This correction is resolved into one of distance along the reference line. The compensating sight indicates the direction of the effective component of drift of the bullet. The pertinent amount of bullet drift depends upon the speed of travel of the firing airplane and the angle at which the gun is pointed relative to the longitudinal axis thereof.

The compensating sight is constructed so that certain references are provided to aid the gunner in making the proper magnitude of correction. For example the point 'I of the arrow may represent full deflection of the sight for an abeam shot at a speed of 100 knots for the firing aircraft. The point 8 of maximum width of the barb of the arrow represents %th of this amount and the pin 9 on the face of the arrow represents 1/2 of this amount. Interpolations between these reference marks can easily be made for various speeds. These reference marks also may be used as a means of making the proper correction for varying angles of fire at a constant speed, or used to solve firing problems involving both factors. At a fixed speed of the ring aircraft the magnitude of correction will decrease as the gun is pointed away from an abeam position, and a zero reference correction will be used when the gun is fired either directly ahead or directly astern. In such latter cases the bead 3' mounted on the post would be centered in the rear peep sight ring I2, instead of any part of the arrow. The fundamental principle of use of the compensating sight is that when the gun is trained through an arc of fire from a position directly ahead or astern toward an abeam position, the arrow is constantly drawn out from the center of the rear peep sight I2. The point 'I of the arrow reaches the maximum position of withdrawal only when the gun is pointed directly abeam, at the designed speed of the sight, for instance 100 knots, or at a lesser angle when the aircraft speed exceeds this figure.

In using the two sights, the gun should be so aimed at the target that the center line of the arrow intersects the center of the peep sight I2. The penetration of the arrow silhouette of the compensating sight into that of the rear peep sight is governed by the combination of the speed of the firing airplane and the angle at which the gun is pointed relative to the longitudinal axis thereof. The penetration of the arrow silhouette into that of the peep sight increases as the speed decreases and as the angle between the axis of the firing airplane and the gun decreases.

The firing problem represented in Figures 4, 5, and 6 involves a ring airplane I3 flying level at a given speed in the direction indicated by the arrow. The target airplane I4 is also flying level, and at the same level as the ring airplane, head-on toward the gunner I5. The arrow is maintained horizontal by the action of the airstream on the vane. Assuming the speed of the firing airplane to be 150 knots and the speed of the bullet to be 2600 feet per second, the bullet drift component is 253 feet per second. It can, therefore, be readily seen that bullet drift is an important item in accurate firing and must be compensated for.

The sighting arrangement for the problem involving a 150 knot speed is shown in Figure 5. Inasmuch as the target is flying directly toward the gunner, it may be treated as a stationary target. Thus the target I4 is centered in the peep sight I2. The center line of the arrow intersects the center of the peep sight I2 and the point 'I is just barely removed from Contact with the outer surface of the peep sight.

When the ring airplane is travelling at a lesser speed, for instance, 100 knots, the proper sighting arrangement for the problem of Figure 4, is as shown in Figure 6. Here the target is again centered in the peep sight and the center line of the arrow intersects the center of the peep sight, but the point l of the arrow is also centered in the peep sight. The disposition of the muzzle of the gun in the latter case is such that the target is given less lead because 0f the decrease in speed of the firing airplane from 150 to 100 knots and a consequent decrease in bullet drift.

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566mm HG( The axis of the arrow being parallel to the bore of the machine gun causes the compensating sight to always indicate the direction of the effective component of the drift of the bullet. This is because the vane of the arrow is operated by the component of the airstream velocity which acts in the opposite direction to the bullet drift. 'I'he diagram in Figure 4 indicates in dotted lines the apparent bullet path and the actual bullet path as well as the component of bullet drift. In this case the bullet drift and the effective component of bullet drift are the same.

The movement of the compensating sight is limited to rotation about its single horizontal axis 3. As long as the gun barrel is held parallel with the longitudinal axis of the airplane, fore or aft, the bead 3 is used as the reference point and the position of the arrow is of no concern as no compensation for bullet drift is required. However, when the gun is moved in this plane, or in other words, a plane horizontal with respect to the disposition of the airplane, to a point where it is at an angle to the longitudinal axis of the airplane, the vane trails in the wind and moves the arrow so that it points straight ahead. This is desirable as the arrow must provide the proper reference line along which the bullet drift must be compensated for. The magnitude of the necessary compensation for aiming purposes is simply a matter of estimating the speed of the ring airplane and the angle that the gun is pointed with respect to the longitudinal axis of the ring airplane. The gunner may then readily select the proper reference point of the arrow and align it with the ring sight. The full length of the arrow is available for this purpose. In the conventional universally mounted wind vane sight the linkage mechanism is located at a level considerably below the bead and there is no line of reference or any point of reference other than the bead itself.

Another type of problem is shown in Figure 7. Here the firing and target airplanes are flying on diverging courses and the target airplane is positioned abaft the beam and upwardly with respect to the ring airplane. Such a condition brings in two other factors that must be considered, namely, the speed of the target airplane relative to the ring airplane and the change in the direction of the effective component of bullet drift.

In the illustrations in Figures 8 and 9, the arrow is shown swung about its pivot to point upwardly. This is due to the fact that the gun is being trained abaft the beam and upwardly with respect to the longitudinal axis of the ring airplane. The calculations with respect to the speed of the firing airplane and the angle aba-ft the beam remain analogous to those mentioned in connection with the problems of Figures 5 and 6. The angle at which the gun is pointed upwardly with respect to the longitudinal axis of the airplane is a factor to be considered in compensating for bullet drift. The wind governed front sight in assuming the upwardly inclined position relative to the mounting post indicates the direction of the acting component of bullet drift and provides a correct reference line along which the magnitude of bullet drift is ascertained and compensated for. It is to be understood that the vane at all times trails with the wind, insofar as its horizontal pivot parallel to the bore of the gun permits. The acting component of the slipstream, or wind, past the gun barrel is parallel to the bullet drift but opposite in direction. The vane trails with the -acting component and the front portion of the arrow points in exactly the opposite direction, and therefore can be used as a measuring device for establishing the proper sight compensation.

Assuming the speed of both of the airplanes to be 150 knots, the center line of the arrow should intersect the center of the peep sight and the arrow should penetrate the peep sight suiiiciently to compensate for the bullet drift in the direction indicated for the predetermined speed of the ring base and the angular disposition of the gun relative thereto. In positioning the gun to bring about this alignment it is also necessary to align the sights so that at the instant the gun is fired the target airplane is positioned on the proper deflection ring and moving toward the center of the peep sight ring in order to compensate for the speed of the target airplane as fully disclosed in my aforementioned copending application. For instance, as shown in Figure 8, the target is brought into such alignment with the ring sight that it is just barely within the intermediate ring Il. The barb 8 of the arrow of the wind vane sight is barely buried in the outer surface of the peep ring. This sighting alignment is computed for an angle of abaft the beam and 35 upward in relation to the longitudinal axis of the ring airplane. The bullet drift and the effective component of bullet drift differ in this case, as indicated by the dotted lines, because of the angle at which the gun is pointed with respect toits moving platform.

With the same conditions prevailing as described in connection with Figure 8, except as to the speed of the ring airplane, Figure 9 represents the proper sighting arrangement when the speed of the firing airplane is 100 knots. Here the barb 8 of the arrow is centered in the peep sight and the disposition of the target airplane remains the same as shown in Figure 8.

The foregoing illustrations are merely examples of the wide use to which the improved wind vane sight may be put. The usual allowance must be made for target speed by using the different speed rings of the rear sight in the customary manner as herein referred to and as fully described in the aforementioned copending application.

I claim:

1. In apparatus for sighting a gun adapted to be red at a target from a moving base and being angularly movable on said base, sighting means for automatically indicating the direction of the eifective component of bullet drift irrespective of the angular disposition of said gun relative to the direction of motion of said moving base, said sight means comprising a sighting member mounted for rotation only about a single axis parallel to the barrel of said gun, a Vane on said member responsive to the air stream induced by movement of said base for positioning said member, and a plurality of reference points for use in determining the magnitude of the correction to be made along said sighting member so as to compensate for the changes in the forces determining the actual bullet path.

Y 2. In an apparatus for sighting a gun adapted to be fired from a moving base and being angularly movable on said base, a gun sight comprising a support movable with the gun, a sighting member rotatably mounted thereon about a single axis parallel to the barrel of said gun, a vane on said member responsive to movement of said base for positioning the member to provide a line of reference in the direction of the acting component of bullet drift, a plurality of spaced indicating means on said movable sighting member for use in determining the magnitude of the correction to be made for said bullet drift, and sighting means spaced from said sight and movable with said gun providing a xed reference point for positioning said gun relative to said target irrespective of the movements of said movable sighting member.

3. In an apparatus for sighting a gun adapted to be red from a moving base, a gun sight comprising a support and a sighting member rotatably mounted thereon about a single axis fixed substantially parallel to the barrel of said gun, and means carried by said member and responsive to the airstream component so as to position said sighting member to automatically indicate the direction of the effective component of the bullet drift, said means comprising a wind vane.

4. In apparatus for sighting a gun adapted to be fired from a moving base, the combination of a support secured to the gun, an axis on the support which is in a xed position parallel to the axis of the gun, an elongated sighting member mounted on the support for movement only about said axis as a pivot, indications spaced lengthwise on said member from the axis, and

ymeans on said member responsive to the commovement of the base for positioning it about said axis.

5. In apparatus for sighting a gun movably mounted on a moving base, the combination of a support movable with the gun, an elongated sighting member mounted on the support for movement only in one plane which is substantially normal to the bore of the gun, and a vane on the member rendering it responsive to the component of the air stream velocity induced by the movement of the base, the resulting position of the member serving to indicate the direction of the effective component of the bullet drift.

6. In a sight for a gun movably mounted on a moving base, the combination of a support having a xed axis substantially parallel to the bore of the gun and movable therewith, an elongated sighting member pivoted intermediate its ends on said support about said axis for movement in a plane normal thereto, and a vane on one end ofv said member for effecting movement thereof about said axis in response to the air stream induced by movement of the base, said movement of the member resulting in a position providing an indication with its opposite end of the direction of the acting component of the bullet drift, irrespective of the angular disposition of said gun with respect to the direction of motion of said base.

JOHN P. GATY. 

